Purification of pentaerythritol



Patented Sept-1.59, i944 UNITED STATES PATENT OFFICE PURIFICATION OF PENTAEBYTHBITOL William Frederick Filbert, Woodbury, N. J., as-

signor to E. L du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 10, 1942, Serial No. 468,490

4Claiml.

0., whereas pentaerythritol containing as much as di-pentaerythritol melts at about 235 C. Pure di-pentaerythritol has a melting point of 221 C. Technical pentaerythritol melts between about 235 and 250 0., depending on the percent of di-pentaerythritol present. Refined pentaerythritol melts between about 250 and 260 0., likewise varying with the percent of di-pentaerythritol present. I

Appreciable differences in the quality of pentaerythritol tetranitrate produced is due to the purity of the pentaerythritol used. Nitration of low grade pentaerythritol, that is, pentaerythritol containing a substantial amount of dipentaerythritol, results in operating difllculties and in the production of a pentaerythritol tetranitrate of uncontrollable and inferior quality. Therefore, there is a definite relationship between the quality of the pentaerythritol nitrated and that of the resulting pentaerythritol tetranitrate.

-An object of this inventiomis a process for obtaining pentaerythritol of a higher degree of purity from a mixture containing pentaerythritol and certain impurities, primarily di-pentaerythritol. Another object is a method to free (pentaerythritol of its impurities in order to insure a uniform and highly pure product upon nitration of said pentaerythritol. A further object is a technical or other low grades of pentaerythrltol by sublimation followed by recrystallization of the sublimate from water. My invention is in part based upon my discovery that, if impure pentaerythritol'with a melting point as low as 190 to 210 0. is sublimed at about 250 0. and

at from about 0 to 35 mm. pressure in a sublimation apparatus, followed by recrystallization of the sublimate eitherat atmospheric pressure or under vacuum from water at a temperature of about 60 to 75 0., a high quality pentaerythritol is produced which meltsbetween 245 and 260 0.

- ucts which accompany the pentaerythritol into process for the production of high quality penta- 'erythritol from impure pentaerythritol, thus This remarkable purification by vacuum sublima tion followed by recrystallization from water in vacuo is achieved because of the fact that d1 pentaerythritol is the principal impurity in pentaerythritol. molecular weight than the latter, vthe pentaerythritol sublimes and leaves di-pentaerythritol as a residue. ,The subsequent recrystallization from water removes volatile decomposition prodthesublimate and are responsible for the instability of the nitration mixture in the production of pentaerythritol tetranitrate.

The example hereinbelow is given in order to make my invention more readily understood and is not to be construed as a limitation thereon.

One hundred grams of contaminated pentaerythritol, containing about10% of impurities and having a melting point between 190 and 210 0., was introduced into a sublimation apparatus comprising a glass sublimation chamber connected by a ground-glass joint through a short length of wide diameter tubing to a watercooled glass receiver, said chamber being maintained at a temperature between 240 and 270 0. by a partially insulated air bath, and from 0 to 35 mm, pressure for one to three hours, or until sublimation is discontinued. The sublimate of 97.5% purity was dissolved in an excess of distilled water and the pentaerythritol recovered by vacuum crystallization at a temperature of about 0. This gave a pentaerythritol of 0.002% ash content and a melting point of 245 to 260 0.

A particular advantage of the process of the present invention is that it is an economical method for the purification of pentaerythritol. Furthermore, it enables the production of a high quality pentaerythritol tetranitrate from a relatively low quality pentaerythritol. A further advantage of my invention is that it provides a means for controlling the uniformity of pentaerythritol tetranitrate produced from vari- Since the former has a higher one low grades of pentaerythritol. Keeping in mind the fact that the cost of refined pentaerythritol, which has been desired for the manufacture of pentaerythritol tetranitrate because of the quality of the product produced therefrom and the safety of the nitration operation, is approximately twice that of technical pentaerythritol, and also bearing in mind the fact that heretofore the technical product has been less satisfactory for use in the manufacture of pentaerythritol tetranitrate because of the impurity of said pentaerythritol, these and other advantages and the importance of my invention will be more fully appreciated.

Although hereinbefore I have made an eflort to render my invention more readily understood by describing it in detail and citing specific embodiments thereof by way of examples, it is to be understood that said specific disclosures and the discussion of the theories or principles underlying my process are for the purpose of clarity only and are not to be construed as a limitation on this invention as otherwise more broadly made of said process may be varied so long as the desired result is achieved. Furthermore, other alterations in the process such as composition, concentration, or quantity of the materials used, as would occur to one skilled in the art, may be made. I do not intend to be limited, therefore, except as this invention is claimed hereinafter.

I claim:

1. The process forpurifying pentaerythritol, which comprises subliming said pentaerythritol at a temperature between about 240 and 260 C. and at a pressure between about 1. and 35 mm.; recovering the sublimate and dissolving the same in an excess of water; and recrystallizing said pentaerythritol by concentrating the solution at a temperature between about 50 and 70 C. and

melting point pentaerythritol from an impure pentaerythritol contained in a mixture consisting essentially of pentaerythritol and 'di-pentaerythritol, which process comprises subliming said pentaerythritol at a temperature between about 240 and 260 C. and at a pressure between about 1 and 35 mm. until sublimation is substantially complete; recovering the sublimate and dissolving the same in an excess of distilled water; and recrystallizing said pentaerythritol by concentrating the solution at a temperature between about and C. and at a pressure substantially less than atmospheric.

3. The process for purifying pentaerythritol having a melting point between about 190 and 250 (3. contained in a mixture consisting essentially of pentaerythritol and di-pentaerythritol, which comprises subliming said impure pentaerythritol at a temperature between approximately 240 and 260 C. and a pressure between about 0 and 35 mm.; recovering the sublimate and dissolving the same in an excess of distilled water, and recrystallizing said pentaerythritol by concentrating said solution at a temperature between about 50 and 70 C. and at a pressure less than atmospheric.

4. The process for separating pentaerythritol contained in a mixture consisting essentially of between about and pentaerythritol and between about 5 and 20% di-pentaerythritol,

WILLIAM FREDERICK mam. 

